Lorena Ochoa, who has finished in the top 10 the last two years, joined Rosie Jones, who is in search of her first major, and Catriona Matthew in second place at 5-under-par 67.
Michelle Wie, the 14-year-old phenom who played in the final group on Sunday in last year's event, birdied two of her last three holes to shoot a 3-under 69.
'I played pretty good, I guess,' said Wie, who played in the PGA Tour's Sony Open in Hawaii earlier this season. 'My driving could have been a little bit better. But I'm still happy the way my score turned out to be.'
Wie collected two birdies in her first five holes but a poor drive at the par-5 ninth led to a bogey. She rebounded at 16 with a nine-foot birdie putt and closed her round with a seven-footer for birdie on the last hole.
While Wie is certainly the future of women's golf, the woman who is currently the top player struggled a bit on Thursday.
Annika Sorenstam traded a birdie for a bogey on the front nine but birdied the 18th to polish off a round of 1-under-par 71.
'I had a hard time finding my swing,' said Sorenstam, a two-time winner of this event who is tied for 19th place. I fought well and to come in under par, I'm pretty happy about that.'
Sorenstam struggled off the tee on Thursday and never put herself in good position to make birdies. Sorenstam, who won last week's Safeway International, stated one of her goals this season was to win the single-season Grand Slam and admitted she was nervous on the first tee.
'I don't know if I was getting too excited because it was a major or what,' said Sorenstam. 'If I'm nervous on the first tee it's going to be a long year.'
The story on Thursday was the 17-year-old whom LPGA commissioner Ty Votaw allowed to qualify for the LPGA Tour this season despite restrictions on players under the age of 18.
'There's nothing that could be better for me to do,' said Song, whose twin sister, Naree, is playing on the Futures Tour. 'It surely beats school. This has been my dream to play out here on tour.'
Song broke out of the gate quickly on Thursday. She drained a short birdie putt at the par-5 second, then hit a spectacular 9-iron to a foot for a tap-in birdie at the sixth.
Song collected one additional birdie before making the turn. At the 168-yard, par-3 eighth, she hit a 6-iron to 13 feet and cashed in on the putt to make the turn at 3-under 33.
On the back nine, Song continued her fine iron play. At No. 10, Song knocked an 8-iron to six feet to set up birdie. The same club netted the same result at the 15th as Song ran home a six-footer to reach 5 under for the championship.
Song tallied her final birdie of the round at the par-5 closing hole. She laid up with her second, then wedged her approach to five feet, where she holed the putt to go one ahead of the field.
'This tournament is one of my favorite tournaments out on tour,' said Song, who shot a 68 in the third round of the 2000 event, when she tied for 10th. 'I'm very comfortable here. I played this event four times. I know the course pretty well.'
Song has made the cut in all four of her appearances in this event. Despite Wie's publicity over the past few years, Song played well as an amateur, including a fifth-place finish in last year's U.S. Women's Open.
Two former champions, Dottie Pepper and Karrie Webb, are knotted in fifth place at 4-under-par 68.
Wie was joined in seventh by Kelly Robbins, Jung Yeon Lee and Candie Kung.
Laura Davies, who needs a win this week to join the Hall of Fame, opened with a 1-under 71 and is part of the group with Sorenstam in 19th. Se Ri Pak, the second player in the world, was a shot further back at even-par 72.